Vector control is a perennial problem in countries situated in tropical and sub-temperate climate zones where insects such as mosquitoes, houseflies, cockroaches, etc. could spread life-threatening diseases, some of which are contagious. The health authorities in developing and under-developed countries are faced with difficult tasks of administering effective vector control programmes within tight budgetary constraints especially in situations where they have to reach out to rudimentary settlements in remote areas, which because of the geographical spread, are costly to administer. The cost effectiveness of these programmes is of paramount importance in controlling outbreak of diseases. Lower spending on preventive measures may lead to higher cost in containing the outbreak of a disease, besides causing politically unacceptable public fear and protests and even social unrest. For instance, in sparsely populated rural areas, the use of fogging method in controlling the population of mosquitoes as a means of controlling the spread of diseases such as dengue fever and malaria are costly and ineffective.
In delivering a chemical insecticide, another consideration is the health hazard on the populace. Yet another consideration is the method to be deployed, taking into consideration the ambient especially home dwellings, food production factories and so on.
It was observed that insects rest and crawl on walls and surfaces of a building. Coating the interior and external walls and surfaces of a construction such as dwellings, hospitals, restaurants, etc. with insecticide is therefore a cost effective way in exterminating insect pests, especially in remote rural areas. However, in buildings where aesthetic appearance is also considerations, the mere applications of insecticide on surfaces of buildings are not a palatable solution. To overcome this shortcoming, emulsion paint impregnated with insecticide was developed. In this way, paint composition served the dual purposes of improving the adiabatic characteristic and beauty of construction as well as serving as a very simple but effective mean of delivering a chemical insecticide for the control and elimination of insect pests especially those in houses, food processing and production factories, hospitals, ships, etc.
Research on acquiring paint compositions which can be applied to every construction and having a sufficient insecticidal effect has been continued for a long time, and various examples are exemplified below.
U.K. Patent application (Publication No. 2142239), published on 16 Jan. 1985 discloses a paint formulation containing insecticides such as pyrethrins and cholorpyrifos. The insecticides are brought to the surface and locked by polymers in said paint system and held in even distribution. Insects of common household pests absorb dosages of the insecticide by entering into contact with the painted surfaces and subsequently die.
European Patent application (Publication No. 0859035), published on 19 Aug. 1998 discloses a spray type insecticidal paint which has long lasting insecticidal effects by contact against various insects but is not harmful to human and warm-blooded animals. The main insecticidal ingredient used is selected from the pyrethroid insecticides such as deltamethrin, permethrin and cypermethrin.
In addition to paint having an insecticide as an active ingredient, paint containing insect repellent has also been formulated. For example, U.S. Pat. No. 5,843,215, published on 1 Dec. 1998 discloses insect repellent paint containing natural plant secondary compounds which are not harmful to the environment or human beings, as an insect repellent component. The plant secondary compounds include Cuminaldehyde, Pinene, Limonene, Eucalytol, Perilladehyde, Linalool, Tumeric oil, Cinnamon oil, and a mixture thereof. These compounds function is to repel insects. A paint varnish disclosed in this patent can be advantageously utilized as a package of foodstuffs.
One of the main problems encountered in paint composition containing insecticides is that the numerous effective insecticidal active ingredients are decomposed by the mitochondrial non-specific oxidative enzymes of the insects so rapidly that the exerted effect is very low. Accordingly the insecticide efficacy is not maintained when the insects developed resistance to the insecticides.
Research on overcoming the development of resistance to insecticides in insects has been continued for a long time and various literature have described the use of piperonyl butoxide as an agent to inhibit the rapid inactivation of the active ingredient in insecticidal combinations.
For example, U.S. Pat. No. 4,524,068, published on 18 Jun. 1985 discloses inclusion complexes of piperonyl butoxide and cyclodextrin, compositions containing them, processes for their preparation and the use of the complexes in insecticidal or fungicidal combinations to synergize the activity of pyrethrines, synthetic pyrethroides or organophosphates.
U.S. Pat. No. 5,883,112, published on 16 Mar. 1999 discloses a synergistic composition comprising pesticidal 5-amino-4ethylsulfinyl-1-arylpyrazoles and piperonyl butoxide, compositions containing them, processes for their preparation and their use as insecticides.
The synergistic effect of piperonyl butoxide and other similar synergistic components manifests itself in the fact that the said agent inhibits the rapid inactivation of the active ingredient by the oxidase enzymes of mixed function found in the insects. The said synergistic agents are useful not only in combination with insecticides but also with fungicides and they are capable of increasing the effect of the active ingredient by ten to fifty times.
As described above, various methods have been developed separately to produce paints containing insecticides on the one hand and insecticidal combinations containing piperonyl butoxide as a synergist on the other hand. However, the inclusion of piperonyl butoxide as a synergist in paint compositions containing insecticides has not been described in any of the prior art documents. In recognition of the situation, the present inventors have earnestly investigated and consequently developed paint compositions containing both insecticides and piperonyl butoxide as a synergist. The paint thus developed according to this invention is found to be effective in overcoming the development of resistance to insecticides in insects.